When considering the overhead line safety margins it is obvious that the key information is the conductor temperature, because it has an influence on all physical characteristics.
Any further calculations like ampacity or sag depend on conductor temperature, that’s why measuring and not calculating the conductor temperature is so important. With such information, the operator can monitor when a specific line is approaching its temperature limit. But we must take into account, that the same conductor temperature in winter or in summer period reflects the completely different current situation. The current conductor temperature alerts the operator if it’s approaching temperature limit, because it takes into account momentary influences (current, wind, solar radiation) that reflect on the line temperature.